This work involves the study of Mossbauer spectroscopy, at low temperatures and over a range of magnetic fields, of heme proteins and related model compounds. Emphasis is placedon hemoglobin and myoglobin and their physiologically relevant states, but work is contemplated on related proteins and related but non-physiological states. Work is in progress in several areas. The temperature dependence of quadrupole interaction and absorption line shape of a heme model has been measured and accounted for in terms of thermally induced eelaxation of the oxygen molecule between different orientations. Similar work is in progress of hemoglobin and myoglobin. The state of deoxymyoblogin has been examined by means of Mossbauer measurements in high magnetic fields in the temperature range from 4.2 K to 195 K. The proportionality tensor between internal and applied magnetic field, and the sign and asymmetry parameter of the electric field gradient has been determined. In combination with published single-crystal Mossbauer measurements these have been interpreted to provide the orientation of the electric field gradient with respect to the heme plane. Similar work is being done on hemoglobin and on model compounds. A large effort is being made to account for the myoglobin, hemoglobin, and model compound spectra, and susceptibility where available, in terms of a crystal field approximate model of the iron site. Work in progress also involves correlation of Mossbauer and EPR data on low spin ferric heme compounds and hemoglobin compounds, and their interpretation in terms of a low symmetry crystal field model. Present and future activity also involves investigation of unusual (3/2) spin states in model compounds.